1. Field of the Invention
The present invention generally relates to discharge tubes and, more particularly, is directed to a discharge tube for use with display devices.
2. Description of the Prior Art
Conventional discharge tubes for use with display devices will be described hereinafter with reference to FIGS. 1 to 3.
FIG. 1 of the accompanying drawings shows a conventional DC -plasma display panel (PDP). As shown in FIG. 1, a plurality of parallel striped cathodes 7 are deposited on a rear glass panel 6 according to a thick film technique such as a screen printing or the like. On a front glass panel 1 that constructs a tube together with the rear glass panel 6, there are deposited a plurality of parallel striped transparent anodes (made of ITO (indium tin oxide)) 2 at a right angle with respect to the cathodes 7. Barrier ribs 12 that prevent discharge from being spread are deposited on the front glass panel 1 or on the rear glass panel 6 so as to be located at each spacing between the adjacent anodes 2 according to the thick film technique. A discharging gas is sealed into the tube composed of the front glass panel 1 and the rear glass panel 6.
FIG. 2 of the accompanying drawings shows a conventional AC-PDP. As shown in FIG. 2, a plurality of parallel striped Y electrodes 14 are deposited on the rear glass panel 6 according to a thick film technique such as screen printing and so on or a thin film technique such as vapor deposition, etching or the like. On the front glass panel 1 that constructs a tube together with the rear glass panel 6, there are deposited a plurality of parallel striped X electrodes 13 at a right angle with respect to the Y electrodes 14 according to the thick film technique such as screen printing and so on or the thin film technique such as vapor deposition, etching or the like. The plurality of Y electrodes 14 and the plurality of X electrodes 13 are respectively covered with insulating layers 15b, 15a and protecting layers 16b, 16a are deposited on the insulating layers 15b, 15a, respectively. The AC type PDP does not need barrier ribs because the discharge is difficult to be diffused.
FIG. 3 of the accompanying drawings shows a conventional hybrid-PDP (see Japanese Published Patent Publication No. 376468). As shown in FIG. 3, a plurality of address electrodes 22, 23, each having a self-scanned function based on the DC discharge, are formed on the rear glass panel 6 to be intersected at a right angle one another. A semi-AC memory unit comprises a transparent full electrode 17 disposed on the front glass plate 1. and which establishes discharge spaces between it and the address electrodes 22, 23 of the rear glass panel 6 through a plurality of apertures and a plurality of aperture metal electrode plate 20 having apertures which are opposed to the transparent full electrode 17. Insulating substrates 24 are disposed on each spacing between the adjacent address electrodes 22, and the transparent full electrode 17 is covered with a transparent insulating layer 18. Barriers 19, 21 are respectively disposed between the aperture metal electrode plate 20 and the transparent insulating layer 18 and between the aperture metal electrode plate 20 and the insulating substrate 24. The above elements thus arranged are sealed into a tube formed of the rear glass panel 6 and the front glass panel 1 and containing therein discharge gas.
According to this hybrid-PDP, the electron, generated due to discharge between the address electrodes 22, 23, is supplied to the semi-AC memory unit side by a voltage applied to the aperture metal electrode plate 20 so that AC-discharge is maintained between the transparent full electrode 17 covered with the transparent insulating layer 18 on the front glass panel 1 and the aperture metal electrode plate 20. The hybrid-PDP could simplify a circuit owing to the self-scanned function thereof and increase a brightness owing to the memory function thereof.
The conventional DC-PDP shown in FIG. 1 is simple in structure and is driven to display an image by simultaneously applying a signal to the plurality of anodes 2 and also by sequentially applying a ground potential to the plurality of cathodes 7 in a so-called line sequential driving fashion. Therefore, the driving of the DC-PDP can be simplified. However, the above DC-PDP has no memory function so that, if the number of the anodes 2 and the cathodes 7 is increased in order to increase a resolution, then a luminous brightness is lowered. Moreover, the electrodes are short in service life because a sputtering phenomenon occurs on the electrodes due to the direct ion bombardment,
The conventional AC-PDP shown in FIG. 2 has a memory function based on wall charge caused by the fact that electric charges are accumulated in the insulating layers that cover the electrodes so that, even if the number of X electrodes and Y electrodes is increased in order to increase a resolution, then a brightness can be prevented from being lowered. On the other hand, a complex signal must be applied between the X and Y electrodes in order to write, memorize and erase a signal. Consequently, a driving circuit for the AC-PDP becomes complicated and a manufacturing process for PDP also becomes complicated because the operation range must be widened.
The conventional hybrid-PDP shown in FIG. 3 is apparently complicated in structure and hence cannot be mass-produced. Moreover, this hybrid-PDP suffers from the following shortcomings and disadvantages.
The diameter of aperture through which the discharge spaces of the address electrode side and the memory unit side are coupled must be increased to make the coupling between the two discharge spaces strong so that the hybrid-PDP can be operated reliably. If the diameter of aperture is increased too much, then it is contradictory that the two discharge spaces cannot be separated reliably. When the memory discharge is erased, the wall electric charge accumulated on the insulating layer formed on the transparent electrode of the front glass panel must be erased. In this case, if the diameter of the aperture on the metal electrode plate is small, then it becomes impossible to control the wall electric charge by the address electrode on the rear glass panel side. Further, if the diameter of the above aperture is large, then the stable addressing and the self-scanned function are deteriorated by influences of memory discharge. Furthermore, the aperture metal electrode plate that isolates the address side and the display side of the display panel must be exposed to the gas in order to extract the electrons from the addressing discharge at the scanning section even though a part of the metal electrode plate is covered with the insulating layer or the metal layer is formed on an insulating body instead of the metal plate. Accordingly, due to the insulation of the aperture metal electrode plate from the DC-scanning section and the safe operation, the elements must be separated with high accuracy one another from a structure standpoint, which makes the manufacturing process of the hybrid-PDP more difficult. In addition, since the above hybrid-PDP operates in a semi-AC fashion, the wall electric charge that contributes to the memory function is accumulated only in the address side. Therefore, the memory function is not powerful and the hybrid-PDP needs a high voltage to maintain the memory function.